"The App Store, now with over 100,000 applications available, is clearly a major differentiator for millions of iPhone and iPod touch customers around the world," Philip Schiller, Apple's (NASDAQ: AAPL) senior vice president of worldwide product marketing, said in a statement. "The iPhone SDK created the first great platform for mobile applications and our customers are loving all of the amazing apps our developers are creating."

Though the App Store launched in July 2008, it already boasts more than 2 billion downloads in 20 categories including games, digital books, news, health, business, travel and sports. Since then, competitors including Palm, Google and BlackBerry maker Research In Motion, as well as wireless carriers Verizon and Sprint have tried to catch up with their own app services and storefronts.

The lucrative smartphone sector, which has seen major handset launches over the past six months from Apple, Palm, Motorola and HTC, continues to spawn a thriving ecosystem including mobile applications -- with downloads slated to triple by 2014 -- as well as in mobile advertising and analytics.

Apple's iPhone OS isn't the only game in town, however, as developers are also flocking to Android, the open source mobile platform that's backed by Google (NASDAQ: GOOG) and its partners in the wireless industry.

For example, to help developers see how people are using specific parts of their iPhone and Android applications, the Internet giant just expanded mobile reporting features in Google Analytics.

Mobile app developers can now get the same Google Analytics reports that provide insight into Web site traffic and engagement for their mini-programs running on iPhones and Android-powered handsets.

"As with Web sites, there are two basic categories of user interaction you can track: pageviews and events. Since mobile apps don't contain HTML pages, developers simply determine when their apps should trigger pageview requests. Google Analytics then aggregates this data in the Content reports to display the number of visits, session length and bounce rates. The data gives insight into how your users interacted with the app," Meredith Papp, of the Google mobile ads team, said in a blog post.

Developers can also use the "event tracking" tool to evaluate visitor actions that don't correspond directly to pageviews. For instance, these actions could be views of embedded videos, button clicks or downloads.

"App developers can then use this data to understand which features are most popular and inform decisions about which features should be promoted or prioritized for further development," said Papp.